Silver recovery process

ABSTRACT

Silver is recovered from silver-containing scrap paper (e.g., scrap thermographic office copy paper) by a process which involves conditioning the silver-containing paper (e.g., with hot dilute aqueous sodium hydroxide) to thereby convert the silver in the paper from its usual organic acid salt form (e.g., silver behenate) into a different form of silver (e.g., converted into silver metal or some silver oxide) which is more readily converted into silver cyanide than is the organic acid salt of silver, and simultaneously or subsequently treating the new silver form with a silver-cyanide forming reagent (e.g., a dilute aqueous sodium cyanide solution) to thereby form silver cyanide. Metallic silver can then be recovered from the resulting silver cyanide solution by standard processing (e.g., zinc dust precipitation in the Merrill-Crowe process) as known in the art.

United States Patent Dorenfeld et al.

[ Mar. 14, 1972 [541 SILVER RECOVERY PROCESS [72] Inventors: Adrian C.Dorenfeld; Gust Bitsianes, both of Minneapolis, Minn.

[73] Assignee: Minerals Technology Corporation, Minneapolis, Minn.

[22] Filed: May 12, 1969 [21] Appl. No.: 823,983

[52] U.S.Cl ..75/l07, 75/118 [51] Int. Cl. ..C22b 11/08 [58]FieldofSearch ..75/118,105,106, 107,101, 75/108, 109; 23/183, 61;260/430; 162/8 [56] References Cited UNITED STATES PATENTS 1,281,24910/1918 Crowe ..75/106 1,397,684 11/1921 2,219,781 10/1940 2,273,5692/1942 3,094,417 6/1963 Primary Examiner-L. Dewayne Rutledge AssistantExaminer-G. T. Ozaki Attorney-Merchant & Gould [57] ABSTRACT Silver isrecovered from silver-containing scrap paper (e.g., scrap thermographicoffice copy paper) by a process which involves conditioning thesilver-containing paper (e.g., with hot dilute aqueous sodium hydroxide)to thereby convert the silver in the paper from its usual organic acidsalt form (e.g., silver behenate) into a difi'erent form of silver(e.g., converted into silver metal or some silver oxide) which is morereadily converted into silver cyanide than is the organic acid salt ofsilver, and simultaneously or subsequently treating the new silver formwith a silver-cyanide fonning reagent (e.g., a dilute aqueous sodiumcyanide solution) to thereby form silver cyanide. Metallic silver canthen be recovered from the resulting silver cyanide solution by standardprocessing (e.g., zinc dust precipitation in the Merrill-Crowe process)as known in the art.

13 Claims, No Drawings SILVER RECOVERY PROCESS BACKGROUND OF THEINVENTION In recent years, there has been an increasing trend toward theuse of heatand light-sensitive copy paper. Many papers of this type arecharacterized by surface coatings which contain silver, usually in theform of one of its solid, organic acid salts. Such silver-containingcopy paper can contain varying amounts of silver. The amount of silverin such copy paper can range from 40 to 500 or more troy ounces per ton(i.e., per 2,000 pounds) of coated copy paper. Amounts of from 50-200troy ounces per ton of coated paper are common.

Silver containing copy papers of this type are described in the priorart, and the following US. Pats. are mentioned for purposes ofillustration:

As shown by these representative patents, silver-containing copy papersof this type are typically prepared by coating paper or some othersuitable copy sheet with a normally solid organic acid salt of silver(e.g., silver behenate) and a reducing agent (e.g., 3,4-dihyroxybenzoicacid) which have been mixed in a resinous or polymeric film-formingbinder (e.g., a polystyrene resin).

In the manufacture of such copy paper, a considerable amount of scrappaper is produced (e.g., as a result of making off-specificationproducts, and as a result of cutting and trimming operations). Variousprocesses (e. g., pyrolysis) have been used in efforts to reclaim thesilver present in this scrap paper, but generally the processes are noteconomically and technically suited for the recovery of silver fromscrap paper wherein the silver content of the paper is less than 150troy ounces per ton of scrap paper. Consequently, the silver is notordinarily reclaimed and the scrap paper is usually sold to paperdealers as scrap paper.

SUMMARY OF THE INVENTION We have discovered a process whereby the silverpresent in such silver-containing scrap papers can be economicallyrecovered, even at low silver contents, (e.g., 40-100 troy ounces ofsilver per ton of scrap paper).

Briefly described, our process involves the steps of:

a. Shredding, chopping, or otherwise reducing the scrap paper to amanageable size (e.g., pieces smaller than one square inch) if that isnecessary;

. Forming an aqueous slurry of the scrap paper;

0. Conditioning the slurry with heat, or a combination of heat and achemical conditioning agent, to thereby convert the silver in the scrappaper into a different water immiscible form from which it can bereadily converted into silver cyanide with an alkali cyanide;

. Separating the resulting conditioned slurry into an aqueous phase anda water immiscible phase (e.g., paper P p);

e. Treating the water immiscible phase with an alkali cyanide solutionfor a time sufficient to convert the silver into silver cyanide; and

f. Thereafter recovering silver from the silver cyanide formed in (e) bystandard processing (e.g., by zinc precipitation in the Merrill-Croweprocess). Steps (c) (i.e., the conditioning step) and (e) (i.e., thesilver cyanide forming step) can be performed sequentially as shown orcan be performed simultaneously. If the steps are performedsimultaneously, it is possible to condition the silver-containing paperby the use of heat (e.g., 6585 C.) in the presence of the alkali cyanide(e.g., aqueous sodium cyanide) and without the need for any chemicalconditioning agent. However, if the steps are performed sequentially,the use of a chemical conditioning agent (e.g., sodium hydroxide) ispreferred because it permits a greater degree of silver recovery. Theuse of a chemical conditioning agent in the combination process offersthe added advantage of producing a sparkling white paper residue (as abyproduct of this process).

DETAILED DESCRIPTlON The silver recovery process of this invention ishereinafter described with emphasis on the recovery of silver by asequence of steps that involve the conditioning or pretreating of anaqueous slurry of the scrap paper (preferably with heat and a chemicalconditioning agent) and the subsequent step of leaching or extractingsilver from the conditioned paper with an alkali cyanide. However, theprocess can also be carried out as a combination process in which theconditioning of the paper and silver extraction are simultaneouslyperformed by heating an aqueous slurry of scrap paper and alkalicyanide. The combination process offers certain processing and economicadvantages over the sequential procedure. The combination process isdescribed in more detail, infra, following the description of thesequential process.

The silver-containing paper The present invention is applicable to therecovery of silver from all types of silver-containing paper (or othercopy sheets). Of course all papers are not alike, and the process.should be optimized for any particular paper that is used. The

process is particularly applicable to the recovery of silver fromheat-sensitive copy paper of the type described in the patentspreviously mentioned herein. Such preferred paper characteristically hasa heator light-sensitive coating which contains a silver salt of a fattyacid (e.g., silver behenate) and a suitable reducing agent, togetherwith optional additives.

Although the process can be applied to scrap paper contain ing largeamounts of silver (e.g., 600 troy ounces per ton of scrap paper), it isparticularly well suited for the recovery of silver from scrap papercontaining less than 150 troy ounces of silver per ton of scrap paper.Scrap paper containing from 40-100 (e.g., 60-90) troy ounces per ton ofscrap paper can be efficiently processed by our scrap recovery process.

As used herein, a troy ounce equals 3l.l grams and a ton equals 2,000pounds (i.e., 907.2 kilograms).

It is not essential that the scrap paper which is treated by our processbe shredded, chopped, or otherwise reduced in size. However, the processis significantly more efficient when applied to scrap paper which hasbeen shredded, chopped, pulped or otherwise reduced to a small size.

The conditioning step The conditioning step or treatment of thesilver-containing paper is performed by heating an aqueous slurry of thescrap paper (e.g., 15 parts of water to one part of paper, by weight),in the optional presence of a chemical conditioning agent, to convertthe silver in the paper into a new form (e.g., converted from silverbehenate to silver or a silver oxide) from which the silver can bereadily converted into silver cyanide.

This conditioning or heating step is an essential part of our process.We have not been able to efficiently and economically extract silverfrom scrap paper (e.g., present as silver behenate) with alkali cyanidesolutions at room temperature as might generally by expected. Unless thealkali cyanide solution is heated above 60 C. (e.g., to 6585 C.) orunless the scrap paper is preconditioned with heat or, more preferably,heat and one or more chemical conditioning agents (e.g., sodiumhydroxide), efficient extraction of the silver is not obtained. Heatingalkali cyanide solutions to extract silver is not common since alkalicyanide techniques are generally effective at room temperature (e.g.,20-25 C.) and alkali cyanides (e.g., NaCN) are poisonous.

Water can be added to the scrap paper to fomi a slurry which isthereafter heated or the paper can be added to heated water (e.g., waterat C.). If desired, a chemical conditioning agent can be used in theform of an aqueous solution (e.g., hot dilute aqueous sodium hydroxide)to provide all or part of the water needed to achieve a manageableaqueous slurry of the scrap paper.

If a chemical conditioning agent is not used, the silver-cyanide-formingstep is desirably performed simultaneously with the heating orconditioning step because the alkali cyanide solution (e.g., sodiumcyanide solution) used to form the silver cyanide seems to perform thefunctions of a chemical conditioning agent provided it is heated (e.g.,heated to more than 65 C.). We prefer to use chemical conditioningagents during the heating step because of the improved results which areobtained.

The chemicals which can optionally be used in the conditioning of thescrap paper include all chemicals and mixtures of chemicals which, underthe conditions of the conditioning step, are capable of converting thesilver in the silver-containing scrap paper into a different form ofsilver (usually a different water insoluble form) from which the silvercan readily be converted into silver cyanide with an alkali cyanide.Although silver cyanide (AgCN) is water insoluble, it is soluble inalkali cyanide solutions (e.g., KCN). ln aqueous alkali cyanidesolutions (e.g., NaCN) silver cyanide is believed to be present as thecorresponding sodium salt, i.e., Na [Ag(CN) which is water soluble. Wehave found that sodium hydroxide is particularly well suited as aconditioning agent and we prefer its use. Other materials which can beused as conditioning agents are sodium silicate, soda ash, potassiumhydroxide, potassium silicate, formic acid, Na i- PO 7 H O, ammoniumcarbonate, Na S-9 H O, Na P O','l0H O, and sodium metasilicate. Amongthe various materials which we have tried which are not effective asconditioning agents under the conditions of our testing are sodiumthiosulfate, oxalic acid, and various calcium, barium and magnesiumsalts (e.g., calcium hydroxide). By way of example, when we have usedpercent aqueous sodium hydroxide as the conditioning agent attemperatures of 70l00 C. and thereafter extracted the conditioned paperwith alkali cyanide solutions (e.g., 0.5 percent aqueous sodium cyanide)at room temperature (i.e., 202S C.), we have been able to recover orextract more than 90 percent of the silver present in the untreatedscrap paper. By contrast, when we have proceeded without effectivelyconditioning the scrap paper, we have typically recovered less than 50percent of the silver present in the untreated scrap paper (e.g.,recovered 10-20 percent of the silver).

The temperature of conditioning can vary and is dependent upon suchfactors as the type of scrap paper, the degree of dilution, the strengthand type of the conditioning agent, and the like. In general, we havefound that conditioning temperatures above 60 C. are desirable, andtemperatures of from 65-lO0;C. (e.g., 7085 C.) are normally effectiverliigli er temperatures (efgf, 1 10 C.) can be used, but are not needed.

The aqueous slurry of scrap paper should be heated, desirably with aconditioning agent or in the presence of an alkali cyanide, for a timesufficient to convert the silver in the scrap paper from its salt orsoap form into a different form from which it can be readily convertedinto silver cyanide by means of an alkali cyanide. Ordinarily, thisconversion of of the silver can be visually observed by noting thechange in color of the scrap paper from a normally white color to black.When we have used hot dilute aqueous sodium hydroxide for conditioningwe have found that the scrap paper will turn black almost immediatelyafter being added to the hot (e.g., 75 C.) solution.

in general, we prefer that the conditioning agent be used at suchconcentrations and in such amounts as to completely blacken the scrappaper in less than 1 hour (e.g., in less than 30 minutes), andpreferably to blacken the paper in less than 5 minutes.

Separation of the conditioned paper After conditioning the paper(assuming the process to be run sequentially and not simultaneously withthe cyanide treatment), the slurry of scrap paper is desirably decantedor filtered to separate the aqueous phase from the water insoluble orimmiscible phase.

We have determined analytically that when our process is run properly(as illustrated by the examples which follow), the aqueous phase orfiltrate contains very little silver and most of the silver originallypresent in the untreated scrap paper remains in the water immisciblephase which is typically a wet, pulpy blackish mixture of paper andconditioned silver. For this reason, it is advantageous to make thisseparation. Then, the aqueous phase (which typically amounts to morethan one-half of the slurry) can be recycled for further use ordiscarded.

The cyanide step Next, the water immiscible phase is treated with anaqueous solution of an alkali cyanide. Suitable alkali cyanides includesodium cyanide and potassium cyanide. Aqueous sodium cyanide ispreferred. The water-immiscible phase and the cyanide are permitted toreact to thereby convert the silver into a silver cyanide which issoluble in aqueous alkali cyanide. With mild agitation at roomtemperature, the conversion of the conditioned silver into itscorresponding silver cyanide is usually quite rapid and can normally beaccomplished in less than 30 minutes. However, under some circumstances,this conversion can require up to 24 hours or longer (e.g., 0.5-6hours). The pregnant solution is then separated from the paper residue(e.g., by decantation or filtration).

The silver recovery step Metallic silver is then recovered from thepregnant silver cyanide/alkali cyanide solution by standard techniqueswhich are known to the art (e.g., the Merrill-Crowe process). Forexample, it is known that silver can be recovered from aqueous alkalicyanide solutions by the addition of finely divided zinc powder (i.e.,zinc dust) to a pregnant solution which has been clarified anddeoxygenated. This addition of zinc powder results in the precipitationof metallic silver from solution. The silver and zinc can then beseparated by known techniques (e.g., smelting).

The combination process As previously indicated, the steps ofconditioning the scrap paper and extracting the silver with an alkalicyanide can be combined and carried out simultaneously. For example, theprocess can be carried out by heating an aqueous slurry of scrap paperat C. in the presence of a mixture of sodium hydroxide and sodiumcyanide. The results obtained by the combination process aresubstantially the same (in terms of silver recovery) as those obtainedby the sequential process.

The combination process can be carried out in the absence of anychemical conditioning agent, but silver recovery is generally lower thanwhen a chemical conditioning agent is used. We believe that the reasonwhy alkali cyanide solutions work without any chemical conditioningagent present is that alkali cyanides form basic solutions at elevatedtemperatures (e.g., 85 C.)

After the silver has been extracted from the scrap paper by thecombination process, the silver can be recovered in the mannerpreviously indicated (e.g., separation of the pregnant liquor from thepulpy residue followed by zinc dust precipitation in the Merrill-Croweprocess).

General Information The pregnant solutions from leaching some silverbearing papers (e.g., certain thermographic office paper) contain soapsand other organic materials (e.g., behanates), in amounts whichinterfere with efficient precipitation of silver. These pregnantsolutions are usually yellowish and turbid. Upon the addition ofsufificient quantities of a suitable metal salt (e.g., calcium chloride)a metal soap can be precipitated and coagulated, leaving a clearsolution. This solution is ready for treatment by the standardMerrill-Crowe process.

The barren solution, obtained after precipitation of the silver, can berecycled in the process.

Another method for silver recovery from silver cyanide solution is tooxidize the cyanide to CO and N by the addition of hypochlorite salts,thus precipitating the silver.

The present invention will be further understood by reference to thefollowing specific examples which include a preferred embodiment. Unlessotherwise indicated, all parts and percentages are by weight.

EXAMPLES 1-5 These examples illustrate the conditioning ofsilver-containing scrap paper with heat and a chemical conditioningagent (sodium hydroxide). The examples demonstrate the effect oftemperature on conditioning.

In each example, 375 ml. of 0.5 percent aqueous sodium hydroxide washeated to the designated temperature and 25 grams of scrap paper (3Mtype 209-B) was then added. The resulting slurry was then agitated whilemaintaining the designated temperature, and visual observations of theslurry were recorded.

Example 1 was run at 50 C. No blackening of the paper was observed inthe first 5 minutes of conditioning. After 15 minutes, a few pieces hadblackened. The test was discontinued. However, it is expected thatcomplete blackening of the paper would have eventually occurred.

Example 2 was run at 60 C. Blackening of the paper was observed in 2-3minutes. After 5 minutes, all of the paper was gray-black. After 15minutes, the paper had turned a dark gray-black.

Example 3 was run at 70 C. Blackening of the paper was noted in -20seconds. After minutes, the paper had all turned a good, even black.

Example 4 was run at 75 C. Blackening occurred in 5 seconds. After 15minutes, the paper had all turned a good even black.

Example 5 was run at 80 C. and blackening occurred in 3-5 seconds. After15 minutes, the paper had all turned a good, even black.

EXAMPLE 6 One hundred fifty eight grams of chopped, scrap thermographiccopy paper, containing 82.5 troy ounces of silver per ton of scrap paperwas added to 2,500 ml. of 1 percent aqueous sodium hydroxide solutionand heated. When the temperature reached approximately 75 C., the scrappaper turned black on one side. The heating was continued until thesolution boiled (at approximately 97 C.). Boiling was continued for 5minutes. The mixture was cooled and filtered. Approximately 1,950 ml. ofa brownish-yellow cloudy filtrate were obtained. The wet residue waswashed with 400 ml. of

water.

For purposes of later testing the feasibility of recycling chemicals,the filtrate, wash water, 200 ml. of fresh water, and 3.6 grams ofsodium hydroxide were mixed and used to condition additional scrapsilver-containing copy paper (not part of this example).

Next, the wet residue was agitated for 17 hours at room temperature with1,900 ml. of water and 6 grams of sodium cyanide. The resulting materialwas then filtered in a Buchner funnel to thereby obtain 1,900 ml. of afairly clear, pregnant solution and a wet paper residue which was savedfor later assay. Silver was then recovered from the pregnant cyanidesolution by zinc dust precipitation.

The zinc dust precipitation of the silver from the pregnant cyanidesolution was performed as follows: Each 500 m1. portion of pregnantcyanide solution was filtered through 0.3 cm. depth of a filter aid(Johns Mansvilles Celite) on a N0. 4 Whatman paper to obtain a veryclear pregnant cyanide solution. The clear pregnant solution was thenagitated for 10 minutes under a vacuum of 700 mm. Hg. Next, 0.5 grams ofzinc dust were added and the resulting mixture agitated for 1 hour underthe same vacuum. This mixture was then filtered on No. 4 Whatman paper.The silver was recovered by fire- The recovery of silver by thistechnique was in excess of percent based on the original silver contentof the untreated scrap paper. The wet paper residue (yellowish in color)from the cyanide treatment was then assayed for silver content and foundto contain 5.8 percent of the silver originally present in the untreatedscrap paper. The remaining traces of silver were lost during processing.

EXAMPLE 7 A large batch of scrap silver bearing paper (Minnesota Miningand Manufacturing Company type 209) was homogenized by shredding,chopping and mixing. This paper contained about 62 troy ounces of silverper ton of paper. Twenty five grams of this homogenized paper was thenadded to a mixture of 500 ml. of water and 5 grams of sodium carbonate.The resulting mixture was then heated to boiling and heating wasdiscontinued. On heating, the paper began to blacken rapidly at about 70C. The scrap paper turned completely black in less than 10 minutes. Thismixture was then filtered on a Buchner funnel and the wet residue waswashed twice with 600 ml. portions of water (each time, the wet residuewas repulped and refiltered). The wet residue, after pressing to removea substantial portion of the remaining water, weighed approximately 52grams. Next, this wet residue was mixed with 475 ml. of water and 3.75grams of sodium cyanide. The resulting mixture was then stirred with amixer in a beaker for approximately one-half hour. The mixture was thenfiltered in a Buchner funnel and 430 ml. of filtrate (i.e., the pregnantcyanide solution) was obtained. The pulpy residue was then pressedthrough rolls to remove more water. During rolling, 27 m1. of water wasremoved. The residue was dried at about 105 C. for ten hours. This paperresidue weighed 23.5 grams. The paper residue (yellowish in color) wasassayed and contained 6.8 Troy ounces of silver per ton. The silverextraction was, therefore, about 89 percent.

EXAMPLES 8-13 A series of six experiments were performed to demonstratethe differences in the extent of silver extraction caused by usingvarious concentrations of alkali cyanide.

In each of these six examples, a 25 gram sample of the homogenized copypaper described in example 7 was conditioned for 15 minutes at 80 C. inapproximately 375 m1. of 0.5 percent aqueous sodium hydroxide. Afterconditioning for approximately 15 minutes, the aqueous slurry ofconditioned paper (now black in color) was cooled to room temperature ina water bath. Next solid sodium cyanide was added to the conditionedpaper slurry at room temperature in amounts sufficient to provide theconcentrations hereinafter set forth. The resulting mixture was thenshaken vigorously for 30 minutes at room temperature, followed byfiltration on a Buchner funnel with vacuum assistance. The resultingfilter cake was then washed with two water washes of 100 ml. each. Thefilter cake was then pressed through rollers at 1,000 psi. to removeadditional liquids. The filter cake was then assayed. The silverextraction, based on fire-assay methods was determined by difference.

In Example 8, the concentration of sodium cyanide was 0.5 percent.Silver extraction was approximately percent.

In Example 9, the sodium cyanide concentration was 0.25 percent. Silverextraction was approximately 95 percent.

In Example 10, the sodium cyanide concentration was 0.1 percent. Silverextraction was approximately 95 percent.

In example 11, the sodium cyanide concentration was 0.05 percent. Silverextraction was approximately 95 percent.

In example 12, the sodium cyanide concentration was 0.025 percent. Onceagain, silver extraction was approximately 95 percent.

In example 13, the sodium cyanide concentration was 0.01 percent. Inthis instance, the silver extraction dropped to approximately 42percent.

In each of these examples, the pulpy residues were various shades ofyellow.

EXAMFJE 14 One hundred grams of homogenized scrap silver-containing copypaper was added to 1,500 ml. of hot water (85 C.) which contained 0.5percent sodium hydroxide and 0.5 percent sodium cyanide (based on theweight of the 1,500 ml. of hot solution). The homogenized pulp wasagitated in this hot water for 1 hour. During this time, the hot waterwas permitted to cool. At the end of the hour, the temperature hadreached approximately 40 C. The slurry was then filtered through aBuchner funnel under vacuum. One thousand and fifty milliliters of ayellowish, turbid, pregnant solution was obtained.

Next, the pulpy residue was washed with three water washes (450 ml.).The first was water (after washing) was then added to the pregnantsolution.

The pulpy residue was then dried for 11 hours at approximately 70 C. Thedry weight of the paper residue was 87.5 grams. Upon assay, it was foundto contain 1.6 ounces of silver per ton of paper.

Next, 2.25 grams of calcium chloride was added to 500 ml. of thepregnant solution (to which had been added the first was water). Aprecipitate formed and coagulated. This precipitate was filtered througha No. 4 Watman paper. The filtrate was clear. The precipitate retainedby the filter paper was then washed with five water washes ml.). All ofthe wash water was then added to the original filtrate. The coagulatedprecipitate was then assayed for silver, but did not contain anysignificant amounts of silver.

Next, 1 10 ml. of the filtrate (i.e., the clarified pregnant solution)was placed in a vacuum flask and deaerated under 700 mm. Hg vacuum withagitation until the bubbling which was first observed had ceased. Then,200 mg. of zinc dust was added to the deaerated filtrate and stirred forapproximately five minutes under the vacuum. A metal precipitate formed.The metal precipitate was filtered in a Buchner funnel through No. 4Watman paper. The filter cake was then boiled with 80 ml. of 2 percenthydrochloric acid solution to dissolve the zinc metal in the filtercake. After boiling, the mixture was cooled and filtered as before. Thefilter cake recovered from this filtration was then fire-assayed. Thisfilter cake was found to contain 14.78 mg. of silver. 7

Subsequent analysis showed that each 100 ml. of the pregnant solutioncontained 16.15 mg. of silver. Therefore, the recovery of the silverfrom the pregnant solution was approximately 92 percent.

The pulpy paper residue which remained was very white when compared withthe pulpy paper residues obtained in the previous examples.

What is claimed is:

l. The process of recovering silver from paper which is coated with asilver-containing coating, said process comprising the steps of:

a. forming an aqueous slurry of paper having a coating thereon thatcontains an organic acid salt of silver;

b. conditioning said slurry by heating it above 60 C. in the presence ofa chemical conditioning agent selected from the group consisting ofsodium hydroxide, sodium silicate, soda ash, potassium hydroxide,potassium silicate, formic acid, disodium phosphate, ammonium carbonate,sodium sulfide and tetra sodium phosphate to thereby convert said silverinto a form from which the silver can be readily converted into silvercyanide with an alkali metal cyanide;

c. treating the conditioned slurry with an alkali metal cyanide toconvert the silver into a silver cyanide; and

d. thereafter recovering silver from the silver cyanide.

2. The process of claim 1 wherein said conditioning agent comprisessodium hydroxide, wherein the conditioning of step (b) is performedprior to the treating of step (c), said conditioning being performed ata temperature of about 70-85 C.

3. The process of claim 2 wherein the alkali metal cyanide comprisessodium cyanide.

4. The process of claim 3 wherein the silver present in the untreatedpaper is present as a fatty acid salt of silver.

S. The process of claim 3 wherein the silver in the paper 15 present assilver behenate and wherein the conditioning of step (b) is continueduntil the paper is blackened.

6. The process of claim 3 wherein the silver present in the untreatedpaper is present as silver behenate.

7. The process of claim 6 wherein at least part of the water needed forforming the slurry of step (a) is provided by using aqueous sodiumhydroxide as the conditioning agent of step (b).

8. The process of claim 6 wherein the silver is recovered by zinc dustprecipitation of a pregnant cyanide solution formed during step (c).

9. The process of claim 1 wherein the conditioning of step (b) isperformed simultaneously with the treating of step (c).

10. The process of claim 9 wherein the conditioning and treating areperformed simultaneously by heating the aqueous slurry of paper to atemperature of 70-85 C. in the presence of sodium cyanide and sodiumhydroxide.

11. The process of recovering silver from paper which is coated with asilver-containing coating, said process comprismg:

a. forming an aqueous slurry of a heat sensitive copy paper having acoating thereon which includes silver behenate;

b. heating the slurry above 60 C. in the presence of sodium hydroxidefor a time sufficient to blacken the paper;

c. separating an aqueous phase from the blackened paper;

d. contacting the blackened paper with aqueous sodium cyanide to extractsilver from the blackened paper; thereby forming a solution pregnantwith silver; and

e. thereafter recovering silver from said pregnant solution.

12. The process of claim 11 wherein the extraction of silver with sodiumcyanide is performed at about room temperature.

13. The process of claim 11 wherein silver is recovered by zinc dustprecipitation of the pregnant cyanide solution of step

2. The process of claim 1 wherein said conditioning agent comprisessodium hydroxide, wherein the conditioning of step (b) is performedprior to the treating of step (c), said conditioning being performed ata temperature of about 70* -85* C.
 3. The process of claim 2 wherein thealkali metal cyanide comprises sodium cyanide.
 4. The process of claim 3wherein the silver present in the untreated paper is present as a fattyacid salt of silver.
 5. The process of claim 3 wherein the silver in thepaper is present as silver behenate and wherein the conditioning of step(b) is continued until the paper is blackened.
 6. The process of claim 3wherein the silver present in the untreated paper is present as silverbehenate.
 7. The process of claim 6 wherein at least part of the waterneeded for forming the slurry of step (a) is provided by using aqueoussodium hydroxide as the conditioning agent of step (b).
 8. The processof claim 6 wherein the silver is recovered by zinc dust precipitation ofa pregnant cyanide solution formed during step (c).
 9. The process ofclaim 1 wherein the conditioning of step (b) is performed simultaneouslywith the treating of step (c).
 10. The process of claim 9 wherein theconditioning and treating are performed simultaneously by heating theaqueous slurry of paper to a temperature of 70*-85* C. in the presenceof sodium cyanide and sodium hydroxide.
 11. The process of recoveringsilver from paper which is coated with a silver-containing coating, saidprocess comprising: a. forming an aqueous slurry of a heat sensitivecopy paper having a coating thereon which includes silver behenate; b.heating the slurry above 60* C. in the presence of sodium hydroxide fora time sufficient to blacken the paper; c. separating an aqueous phasefrom the blackened paper; d. contacting the blackened paper with aqueoussodium cyanide to extract silver from the blackened paper; therebyforming a solution pregnant with silver; and e. thereafter recoveringsilver from said pregnant solution.
 12. The process of claim 11 whereinthe extraction of silver with sodium cyanide is performed at about roomtemperature.
 13. The process of claim 11 wherein silver is recovered byzinc dust precipitation of the pregnant cyanide solution of step (d).